Sexual Size Dimorphism and Survival of Male and Female Blackbirds (Icteridae)

Abstract In a between-species comparison of icterids, male survival decreases relative to female survival as the degree of sexual size dimorphism increases. This result is consistent with the hypothesis that male size is limited by survival selection in icterids; the degree of size dimorphism is known to correlate with the degree of polygyny in icterids, however, so the decreased relative survival of males in dimorphic species may be caused by some correlate of polygyny other than large size. Survival estimates based on records of recovery of dead birds show positive correlations between male size and male survival and between female size and female survival, but survival estimates based on recaptures of live birds fail to show such relationships.